Highly fluorinated polymers

ABSTRACT

A method of making a highly fluorinated polymers and resulting aqueous mixtures. The method comprising polymerizing one or more perfluorinated monomers in an aqueous emulsion polymerization in the presence of a polymerizable fluorinated emulsifier to form a perfluorinated polymer. The polymerizable fluorinated emulsifier has the formula X 2 C═CX(CF 2 ) m (CH 2 ) n [O—(CX 2 ) p ] q —[O—(CX 2 ) r ] s −[O—(CX 2 —CX 2 )] t —[(O) w —(CX 2 ) u ] v —[CH 2 ] z —Y. The method also provides for isolating the highly fluorinated polymer and post-fluorinating the isolated highly fluorinated polymer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/646,980, filed May 22, 2015, now allowed, which is a nationalstage filing under 35 U.S.C. 371 of PCT/US2013/071152, filed Nov. 21,2013, which claims priority to U.S. Provisional Application No.61/732,967, filed Dec. 4, 2012, the disclosure of which is incorporatedby reference in its/their entirety herein.

TECHNICAL FIELD

A method for making highly fluorinated polymers using a polymerizablefluorinated emulsifier is described.

SUMMARY

Fluoropolymers, i.e. polymers having a fluorinated backbone, have beenlong known and have been used in a variety of applications because ofseveral desirable properties such as heat resistance, chemicalresistance, weatherability, UV-stability, etc.

A frequently used method for producing fluoropolymers involves aqueousemulsion polymerization of one or more fluorinated monomers using afluorinated emulsifier.

An aqueous emulsion polymerization wherein no emulsifier is used hasbeen described in U.S. Pat. No. 5,453,477, WO 96/24622 and WO 97/17381to generally produce homo- and copolymers of chlorotrifluoroethylene(CTFE). For example, WO 97/17381 discloses an aqueous emulsionpolymerization in the absence of an emulsifier wherein a radicalinitiator system of a reducing agent and oxidizing agent is used toinitiate the polymerization and whereby the initiator system is added inone or more further charges during the polymerization. So-calledemulsifier free polymerization has further been disclosed in WO 02/88206and WO 02/88203. In the latter PCT application, the use of dimethylether or methyl tertiary butyl ether is taught to minimize formation oflow molecular weight fractions that may be extractable from thefluoropolymer. WO 02/88207 teaches an emulsifier free polymerizationusing certain chain transfer agents to minimize formation of watersoluble fluorinated compounds. An emulsifier free polymerization isfurther disclosed in RU 2158274 for making an elastomeric copolymer ofhexafluoropropylene and vinylidene fluoride. However, emulsifier freepolymerizations have some disadvantages such as e.g., large particlesizes.

Thus, the aqueous emulsion polymerization process in the presence offluorinated emulsifiers is still a desirable process to producefluoropolymers because it can yield stable fluoropolymer particledispersions in high yield and in a more environmental friendly way thanfor example polymerizations conducted in an organic solvent.Traditionally, the emulsion polymerization process is carried out usinga perfluoroalkanoic acid or salt thereof as an emulsifier. Thesenon-polymerizable emulsifiers are typically used as they provide a widevariety of desirable properties such as high speed of polymerization,good copolymerization properties of fluorinated olefins with comonomers,small particle sizes of the resulting dispersion can be achieved, goodpolymerization yields (i.e. a high amount of solids can be produced),good dispersion stability, etc., however, environmental concerns havebeen raised with these emulsifiers.

Accordingly, measures have been taken to replace the perfluoroalkanoicacid or salt thereof with alternative emulsifiers having an improvedenvironmental profile as disclosed in U.S. Pat. Publ. No. 2007/0015865(Hintzer et al.). However, such alternative emulsifiers can be expensiveand difficult to make. Additionally, and/or alternatively, thesenon-polymerizable fluorinated emulsifiers may be removed from theaqueous dispersion and waste streams as disclosed in U.S. Pat. No.6,833,403 (Blaedel, et al.). However, the removal adds an additionalprocessing step and/or cost.

Thus, there is a desire to provide an aqueous polymerization methodusing a fluorinated emulsifier, which does not require removal of thefluorinated emulsifier post polymerization, and wherein the resultingaqueous emulsion is substantially free of the fluorinated emulsifier. Inone embodiment, it is desirable to identify a method to manufacturehighly fluorinated polymers that is simple and/or lower cost.

In one aspect, method of making a highly fluorinated polymer isdescribed comprising:

(i) polymerizing one or more perfluorinated monomers in an aqueousemulsion polymerization in the presence of a polymerizable fluorinatedemulsifier to form a perfluorinated polymer, wherein the polymerizablefluorinated emulsifier is selected from:X₂C═CX(CF₂)_(m)(CH₂)_(n)[O—(CX₂)_(p)]_(q)—[O—(CX₂)_(r)]_(s)—[O—(CX₂—CX₂)]_(t)—[(O)_(w)—(CX₂)_(u)]_(v)—[CH₂]_(z)—Y  Formula(I):where X is independently selected from H, F, or CF₃; Y is COOM or SO₃M;m is 0-5, n is 0-5, p is at least 1, q is 0-5, r is 0-5, s is 0-5, t is0-5, u is 0-5, v is 0-5, w is 0 or 1, and z is 0-5; wherein at least oneof m, n, q, s, t, u, v, and z is at least 1; and M is H, an alkalimetal, or NH₄; wherein the polymerizable fluorinated emulsifier (a)comprises at least 1 fluorine atom; (b) is substantially free oftelogenic activity, and (c) is less than 1 wt % based on the totalweight of monomers used;

(ii) isolating the highly fluorinated polymer; and

(ii) post-fluorinating the isolated highly fluorinated polymer.

In one embodiment, the polymerizable fluorinated emulsifier is selectedfrom the group consisting of:CF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—[O—(CF₂)_(r)]_(s)—Y  (II)CF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—[O—(CF(CF₃)—CF₂)]_(t)—[O—CF(CF₃)]_(v)—Y  (III);andCX₂═CX—(CF₂)_(a)—Y  (IV)where X is independently selected from H, F, or CF₃; where Y is COOM orSO₃M, m is an integer selected from 0-5, p is at least 1, r is aninteger selected from 0-5, s is an integer selected from 1-5, t is aninteger selected from 1-5, v is an integer selected from 1-5, and M isH, an alkali metal, or NH₄.

The above summary is not intended to describe each embodiment. Thedetails of one or more embodiments of the invention are also set forthin the description below. Other features, objects, and advantages willbe apparent from the description and from the claims.

DETAILED DESCRIPTION

As used herein, the term

“a”, “an”, and “the” are used interchangeably and mean one or more; and

“and/or” is used to indicate one or both stated cases may occur, forexample A and/or B includes, (A and B) and (A or B).

Also herein, recitation of ranges by endpoints includes all numberssubsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75,9.98, etc.).

Also herein, recitation of “at least one” includes all numbers of oneand greater (e.g., at least 2, at least 4, at least 6, at least 8, atleast 10, at least 25, at least 50, at least 100, etc.).

The goal of the present disclosure is to prepare a highly fluorinatedpolymer dispersion wherein the dispersion is stabilized and issubstantially free of fluorinated emulsifier.

In the present disclosure, an acid-functionalized monomer (hereinreferred to as a polymerizable fluorinated emulsifier) is used, not toimpart different properties onto the resulting final fluoropolymer, butto stabilize the fluoropolymer dispersion. Although not wanting to belimited by theory, it is believed that by adding a small amount of apolymerizable fluorinated emulsifier to an aqueous fluoropolymerpolymerization, these acid-functionalized monomers are able to stabilizethe polymerization, yet not impact the properties of the resultingfluoropolymer. Furthermore, because the acid-functionalized monomers arepolymerized into the fluoropolymer, there may be no need for removal ofthem from the aqueous dispersion and/or the waste water. In a furtherembodiment, the resulting highly fluorinated polymer may bepost-fluorinated to improve the overall end-use properties of thepolymer (e.g., thermal degradation, discoloration, blistering, etc.).

The present disclosure is directed toward an aqueous emulsionpolymerization that comprises perfluorinated monomers and apolymerizable fluorinated emulsifier. It has been found that emulsifiersof Formula (I) are effective in stabilizing the aqueous emulsionpolymerization of fluoropolymers.

The polymerizable fluorinated emulsifiers of the present disclosure arethose that correspond to formula (I):X₂C═CX(CF₂)_(m)(CH₂)_(n)[O—(CX₂)_(p)]_(q)—[O—(CX₂)_(r)]_(s)—[O—(CX₂—CX₂)]_(t)—[(O)_(w)—(CX₂)_(u)]_(v)—[CH₂]_(z)—Ywhere X is independently selected from H, F, or CF₃; Y is COOM or SO₃M;wherein the polymerizable fluorinated emulsifier comprises at least 1fluorine atom. M is H, an alkali metal (e.g., Na, Ca, etc.), or NH₄.Subscript m is 0-6, 0-5, 0-4; 0-3, or even 0-2. Subscript n is 0-6, 0-5,0-4; 0-3, or even 0-2. Subscript p is at least 1, 2, 3, 4, or even 5;and no more than 20, 10, 8, or even 6. Subscript q is 0-6, 0-5, 0-4;0-3, or even 0-2. Subscript r is 0-6, 0-5, 0-4; 0-3, or even 0-2.Subscript s is 0-6, 0-5, 0-4; 0-3, or even 0-2. Subscript r is 0-6, 0-5,0-4; 0-3, or even 0-2. Subscript u is 0-6, 0-5, 0-4; 0-3, or even 0-2.Subscript v is 0-6, 0-5, 0-4; 0-3, or even 0-2. Subscript w is 0 or 1.Subscript z is 0-6, 0-5, 0-4; 0-3, or even 0-2. At least one of m, n, q,s, t, u, v, and z is at least 1.

The polymerizable fluorinated emulsifiers disclosed herein may be intheir acid form or may be a salt, including for example, sodium,potassium, and ammonium salts.

The polymerizable emulsifier used in the present disclosure isfluorinated, therefore, the polymerizable emulsifier, must include atleast 1 fluorine atom. Because the resulting polymers of the presentdisclosure are highly fluorinated, it is desirable that at least 50%,75%, 90%, 95% or even 99% of the carbon-hydrogen bonds of thepolymerizable fluorinated emulsifier be replaced by carbon-fluorinebonds. In one embodiment, the polymerizable emulsifier of the presentdisclosure is perfluorinated (or fully fluorinated).

In one embodiment, the polymerizable fluorinated emulsifier is selectedfrom the group consisting of (i) fluorinated vinyl ethers, (ii)fluorinated allyl ethers, and (iii) fluorinated olefins.

In one embodiment, the polymerizable fluorinated emulsifier is a linearmolecule and does not comprise any branching (e.g., a carbon substituentattached off the main chain of the molecule, e.g., CF₂═CF—O—CF(CF₃)—Y isbranched).

Fluorinated vinyl ethers include those of formulas:CF₂═CF—O—(CF₂)_(p)—O—(CF₂)_(r)—YCF₂═CF—O—(CF₂)_(p)—[O—CF[CF₃]—CF₂]_(t)—O—CF(CF₃)—YCF₂═CF—O—(CF₂)_(p)—O—CHF—CF₂—YCF₂═CF—O—(CF₂)_(p)—O—CHF—YCF₂═CF—O—(CF₂)_(p)—CH₂—YandCF₂═CF—O—(CH₂)_(p)—(CF₂)_(r)—CH₂—Ywhere Y is COOM or SO₃M. M is H, an alkali metal, or NH₄. Subscript r isan integer selected from at least 0 or 1 and at most 6, 5, 4, 3, or even2. Subscript t is an integer selected from at least 0 or 1 and at most6, 5, 4, 3, or even 2. Subscript p is an integer selected from at least1 and at most 6, 5, 4, 3, or even 2.

Exemplary fluorinated vinyl ethers include partially fluorinated vinylethers and perfluorinated fluorinated vinyl ethers such as:CF₂═CF—O—(CF₂)₃—O—CF₂—COOM, CF₂═CF—O—(CF₂)₂—O—CF₂—COOM,CF₂═CF—O—(CF₂)—(O—CF[CF₃]—CF₂)—O—CF(CF₃)—COOM,CF₂═CF—O—(CF₂)₂—(O—CF[CF₃]—CF₂)—O—CF(CF₃)—COOM,CF₂═CF—O—(CF₂)₃—(O—CF[CF₃]—CF₂)—O—CF(CF₃)—COOM,CF₂═CF—O—(CF₂)₂—CH₂—COOM, CF₂═CF—O—(CH₂)—(CF₂)₂CH₂—COOM,CF₂═CF—O—(CF₂)₄—SO₃M, and combinations thereof where M is H, an alkalimetal, or NH₄.

Fluorinated allyl ethers include those of formulas:CF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—O—(CF₂)_(r)—YCF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—[O—CF[CF₃]—CF₂]_(t)—O—CF(CF₃)—YCF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—O—CHF—CF₂—YCF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—O—CHF—YCF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—CH₂—Yandwhere Y is COOM or SO₃M. M is H, an alkali metal, or NH₄. Subscript m isan integer selected from at least 1 and at most 6, 5, 4, 3, or even 2.Subscript r is an integer selected from at least 0 or 1 and at most 6,5, 4, 3, or even 2. Subscript t is an integer selected from at least 0or 1 and at most 6, 5, 4, 3, or even 2. Subscript p is an integerselected from at least 1 and at most 6, 5, 4, 3, or even 2.

Exemplary fluorinated allyl ethers include partially fluorinated allylethers and perfluorinated fluorinated allyl ethers such asCF₂═CFCF₂—O—(CF₂)₃—O—CF₂—COOM, CF₂═CFCF₂—O—(CF₂)₂—O—CF₂—COOM,CF₂═CFCF₂—O—(CF₂)—[O—CF(CF₃)—CF₂]—O—CF(CF₃)—COOM,CF₂═CFCF₂—O—(CF₂)₂—[O—CF(CF₃)]—CF₂]—O—CF(CF₃)—COOM,CF₂═CFCF₂—O—(CF₂)₃—[O—CF(CF₃)—CF₂]—O—CF(CF₃)—COOM,CF₂═CFCF₂—O—(CF₂)₂—CH₂—COOM, CF₂═CFCF₂—O—(CF₂)₂—O—CHF—COOM, andcombinations thereof where M is H, an alkali metal, or NH₄.

Fluorinated olefins include those of formula:CX₂═CX—(CF₂)_(m)—Y andCF₂═CF—(CF₂)_(m)—Ywhere X is independently selected from H, F, or CF₃ and Y is COOM orSO₃M. M is H, an alkali metal, or NH₄. Subscript m is an integerselected from at least 1 and at most 6, 5, 4, 3, or even 2. In oneembodiment, at least one of X in the fluorinated olefin is a H. In oneembodiment, at least one of X in the fluorinated olefin contains a Fatom.

Exemplary fluorinated olefins include partially fluorinated olefins andperfluorinated olefins such as: CH₂═CF—(CF₂)—COOM, CF₂═CH—(CF₂)—COOM,CH₂═CF—(CF₂)₂—COOM, CF₂═CF—(CF₂)—COOM, CF₂═CF—(CF₂)—SO₃M, andcombinations thereof where M is H, an alkali metal, or NH₄.

In one embodiment, the polymerizable fluorinated emulsifier is selectedfrom the group consisting of:CF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—[O—(CF₂)_(r)]_(s)—Y  (II)CF₂═CF—(CF₂)_(m)—O—(CF₂)_(p)—[O—(CF(CF₃)—CF₂)]_(t)—[O—CF(CF₃)]_(v)—Y  (III);andCX₂═CX—(CF₂)_(m)—Y  (IV)where X is independently selected from H, F, or CF₃; where Y is COOM orSO₃M, m is an integer selected from 0-5, except in the case of Formula(IV) where m is an integer selected from 1-5, p is at least 1, r is aninteger selected from 0-5, s is an integer selected from 1-5, t is aninteger selected from 1-5, v is an integer selected from 1-5, and M isH, an alkali metal, or NH₄.

Exemplary polymerizable fluorinated emulsifiers of the presentdisclosure include: CF₂═CF—O(—CF₂)_(p)—O—CF₂—COOM where p is 1, 2, 3, 4,5, or 6; CF₂═CF—CF₂—O—(—CF₂)_(p)—[O—CF₂—(CF₂)_(u)—COOM where p is 1, 2,3, 4, 5, or 6 and u is 0 or 1; CF₂═CF—O—CF₂COOM;CF₂═CF—O—(CF₂)_(p)—O—CF(CF₃)—COOM where p is 1, 2, 3, 4, 5, or 6; andCF₂═CF—O—(CF₂)_(p)—SO₃M where p is 1, 2, 3, 4, or 5; andCF₂═CF—O—(CF₂)_(p)—SO₃M where p is 1, 2, 3, 4, 5, or 6; and M is H, analkali metal, or NH₄.

The polymerizable fluorinated emulsifiers of the present disclosure havenon-telogenic activity meaning that less than 50%, 40%, 30%, 20%, 10%,5%, 1%, or even none of the carbon bonds are to hydrogen. In otherwords, the polymerizable fluorinated emulsifier does not act like achain transfer agent and consequently does not reduce the molecularweight of the resulting polymer. The polymerizable fluorinatedemulsifiers of the present disclosure are polymerized into the polymerbackbone and do not terminate the polymerization.

In the polymerization of the present disclosure, the polymerizablefluorinated emulsifiers mentioned above are used in the aqueous emulsionpolymerization of one or more perfluorinated monomers.

The amount of polymerizable fluorinated emulsifier used may varydepending on desired properties such as amount of solids, particle size,etc. Generally, the amount of polymerizable fluorinated emulsifier iskept to a level, which is sufficient to stabilize the fluoropolymerdispersion. Typically, the amount of polymerizable fluorinatedemulsifier will be at least 50, 100, 200, 300, 400, or even 500 ppm(parts per million) and based on the total amount of perfluorinatedmonomer used. If unnecessarily large amounts of fluorinatedpolymerizable emulsifier are used, the resulting fluoropolymer may bedifficult to coagulate and/or work-up and may also impact the propertiesof the final polymer, for example, thermal stability or discoloration.Typically, the amount of polymerizable fluorinated emulsifier will be atmost 750, 1000, 2000, 4000, 5000, or even 10000 ppm based on the totalamount of perfluorinated monomer used.

The polymerization of the present disclosure is an aqueous emulsionpolymerization, meaning that polymerization occurs in polymer particlesdispersed in water which are electronically stabilized by an emulsifier.Aqueous emulsion polymerization can be carried out continuously inwhich, for example, monomers, water, optionally further emulsifiers,buffers and catalysts are fed continuously to a stirred reactor underoptimum pressure and temperature conditions while the resulting emulsionis removed continuously. An alternative technique is batch or semibatch(semi-continuous) polymerization characterized by feeding theingredients into a stirred reactor and allowing them to react at a settemperature for a specified length of time or by charging ingredientsinto the reactor and feeding the monomers into the reactor to maintain aconstant pressure until a desired amount of polymer is formed. Thepolymerization can be carried out in a standard or conventional vesselused for emulsion polymerization of gaseous fluorinated monomers.

In one embodiment, the polymerizable fluorinated emulsifier is addedcontinuously during the polymerization. Although not wanting to be boundby theory, it is believed that by continuously adding the polymerizablefluorinated emulsifier during polymerization, higher solids can beachieved. It is thought that because the stabilizing polar groups arecovered by growing polymer chains and thus, are unable to contribute tothe colloidal stability, it may be important to constantly havestabilizing polar groups at the polymer surface and thus, thepolymerizable fluorinated emulsifier may be added continuously duringpolymerization. In one embodiment, it is preferable to stop the additionof the polymerizable fluorinated emulsifier prior to the end of thepolymerization, in order to ensure that the polymerizable fluorinatedemulsifier is completely incorporated into the polymer and to avoidtreatment of waste water streams.

In one embodiment, it may be desirable to add a certain monomer to thepolymerization in the form of an aqueous emulsion. For example,perfluorinated co-monomers that are liquid under the polymerizationconditions may be advantageously added in the form of an aqueousemulsion. The emulsion of such co-monomers is preferably prepared usingthe polymerizable fluorinated emulsifier. If a portion of thepolymerizable fluorinated emulsifier is batch-charged prior topolymerization start, it is optional to use “doped” polymerizablefluorinated emulsifiers. Where the doped polymerizable fluorinatedemulsifier are microemulsions with fluorinated, low telogenic, inertliquids with boiling points higher than 100° C. Examples of such liquidsinclude: (i) fluorinated cyclic hydrocarbons, such asoctafluoronaphthalene, octafluorotoluene, hexafluorobenzene,perfluoroperhydrophenantrene (C₁₄F₂₄), perfluoroperhydrofluorene(C₁₃F₂₂), perfluoro decalin (C₁₀F₁₈), perfluoro methyl decalin (C₁₁F₂₀),perfluoro butyl decalin (C₁₄F₂₆), perfluorodimethylcyclohexane (C₈F₁₆),perfluoromethylcyclohexane (C₇F₁₄), perfluorodimethylcyclobutane(C₆F₁₂); (ii) fluorinated polyoxyalkenes of the formulaCF₂═CF—(CF₂)₁—O(R^(a) _(f)O)_(n)(R^(b) _(f)O)_(m)R^(c) _(f), where R^(a)_(f) and R^(b) _(f) are different perfluoroalkylene groups of 3 to 6C-atoms, R_(cf) is a perfluoroalkyl group of 1 to 6 C-atoms, l is 0 orl, m and n are independently 0 to 10 and n+m is >2 or >3, examplesinclude: CF₃—CF₂—CF₂—(O—CF(—CF₃)—CF₂)₂—O—CF═CF₂ (PPVE-3),CF₃—CF₂—CF₂—(O—CF(—CF₃)—CF₂)₃—O—CF═CF₂ (PPVE-4),CHF₂—CF₂—CF₂—(O—CF(—CF₃)—CF₂)—O—CF═CF₂ (HPPVE-2),CHF₂—CF₂—CF₂—(O—CF(—CF₃)—CF₂)₂—O—CF═CF₂ (HPPVE-3); (iii) fluorinatedalkenes of the formula F₃C—C(R^(d) _(f))═C(R^(e) _(f))(R^(f) _(f)) whereR^(d) _(f) and represent R^(e) _(f) independently from each otherfluorine or a perfluorinated or partially fluorinated, linear orbranched alkyl group, preferably a group having from 1 to 6, preferably1 to 3, carbon atoms and R^(f) _(f) represents a perfluorinated, linearor branched alkyl group of 1 to 6 carbon atoms, preferably a methyl,ethyl, propyl or isopropyl group, examples include:C(—CF₃)(—CF₃)═CF—CF₂—CF₃ (HFP-Dimer), andC(—CF₃)₂═C(—CF₂—CF₃)(—CF(—CF₃)₂) (HFP-Trimer); and (iv) fluorinatedpolyoxyalkanes of the formula R^(g) _(f)—O—R^(h) _(f)—O—R^(i) _(f) whereR^(g) _(f) and R^(i) _(f) are independently fluorinated alkyl groups of2 to 5 C-atoms and R^(h) _(f) is a branched perfluorinated alkyl groupof 2 to 4 C-atoms atoms, examples include:CHF₂—CF₂—CF₂—O—CF(—CF₃)—CF₂—O—CFH—CF₃ (HTFEE-2),CHF₂—CF₂—CF₂—O—CF(—CF₃)—CF(—CF₃)—O—CF₂—CF₂—CHF₂, andCF₃—CF₂—CF₂—O—CF(—CF₃)—CF(—CF₃)—O—CF₂—CF₂—CF₃. See for example, U.S.Pat. Publ. No. 2011/0294951 (Hintzer et al.), herein incorporated byreference.

The aqueous emulsion polymerization may be carried out at temperaturesbetween 10 to 100° C., or even 30° C. to 80° C. and the pressure istypically between 2 and 50 mbar, or even 5 to 30 bar. The reactiontemperature may be varied during the polymerization to influence themolecular weight distribution, i.e., to obtain a broad molecular weightdistribution or to obtain a bimodal or multimodal molecular weightdistribution.

The aqueous emulsion polymerization is typically initiated by aninitiator including any of the initiators known for initiating a freeradical polymerization of fluorinated monomers. The initiators of thepolymerization system are selected such that the polymer endgroups arethe same as the polymerizable fluorinated emulsifier; e.g. KMnO₄generates COO⁻ endgroups, while APS/bisulfite systems partially generateSO₃ ⁻ endgroups.

Suitable initiators include peroxides and azo compounds and redox basedinitiators. Specific examples of peroxide initiators include, hydrogenperoxide, sodium or barium peroxide, diacylperoxides such asdiacetylperoxide, disuccinoyl peroxide, dipropionylperoxide,dibutyrylperoxide, dibenzoylperoxide, benzoylacetylperoxide, diglutaricacid peroxide and dilaurylperoxide, and further per-acids and saltsthereof such as e.g. ammonium, sodium or potassium salts. Examples ofper-acids include peracetic acid. Esters of the peracid can be used aswell and examples thereof include tert-butylperoxyacetate andtert-butylperoxypivalate. Examples of inorganic initiators include forexample ammonium- alkali- or earth alkali salts of persulfates,permanganic or manganic acid. A persulfate initiator, e.g. ammoniumpersulfate (APS), can be used on its own or may be used in combinationwith a reducing agent. Suitable reducing agents include bisulfites suchas for example ammonium bisulfite or sodium metabisulfite, thiosulfatessuch as for example ammonium, potassium or sodium thiosulfate,hydrazines, azodicarboxylates and azodicarboxyldiamide (ADA). Furtherreducing agents that may be used include sodium formaldehyde sulfoxylate(sold for example under the trade designation “RONGALIT”) or fluoroalkylsulfinates as disclosed in U.S. Pat. No. 5,285,002 (Grootaert). Thereducing agent typically reduces the half-life time of the persulfateinitiator. Additionally, a metal salt catalyst such as for examplecopper, iron or silver salts may be added. The amount of initiator maybe between 0.01% by weight and 1% by weight based on the fluoropolymersolids to be produced. In one embodiment, the amount of initiator isbetween 0.05 and 0.5% by weight. In another embodiment, the amount maybe between 0.05 and 0.3% by weight. The full amount of initiator may beadded at the start of the polymerization or the initiator can be addedto the polymerization in a continuous way during the polymerization.Preferably the initiator is added until a conversion of monomer topolymer of 70% to 80% is achieved. One can also add part of theinitiator at the start and the remainder in one or separate additionalportions during the polymerization.

The aqueous emulsion polymerization system may further comprise othermaterials, such as buffers and, if desired, complex-formers orchain-transfer agents. Examples of chain transfer agents that can beused include dimethyl ether, methyl t-butyl ether, alkanes having 1 to 5carbon atoms such as ethane, propane and n-pentane, halogenatedhydrocarbons such as CCl₄, CHCl₃ and CH₂Cl₂; hydrofluorocarbon compoundssuch as CH₂F—CF₃ (R134a); alcohols; esters; and the like.

Examples of fluorinated monomers that may be polymerized using thepolymerizable fluorinated emulsifier as an emulsifier: includetetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE),hexafluoropropylene (HFP), dichlorodifluoroethylene, and perfluorinatedalkyl vinyl monomers such as perfluorinated vinyl ethers (PVE) andperfluorinated allyl ethers, perfluoro-5-oxa-hept-6-ene sulphonic acidfluoride (MV4S), CF₂═CFO(CF₂)₅CN (MV5CN), and combinations thereof.

Suitable perfluoroalkyl vinyl monomers correspond to the generalformula: CF₂═CF—R^(d) _(f) or CH₂═CH—R^(d) _(f) wherein R^(d) _(f)represents a perfluoroalkyl group of 1-10, or even 1-5 carbon atoms.

Examples of perfluorovinyl ethers that can be used in the presentdisclosure include those that correspond to the formula: CF₂═CF—O—R_(f)wherein R_(f) represents a perfluorinated aliphatic group that maycontain no, one or more oxygen atoms and up to 12, 10, 8, 6 or even 4carbon atoms. Exemplary perfluorinated vinyl ethers correspond to theformula: CF₂═CFO(R^(a) _(f)O)_(n) (R^(b) _(f)O)_(m)R^(c) _(f) whereinR^(a) _(f) and R^(b) _(f) are different linear or branchedperfluoroalkylene groups of 1-6 carbon atoms, in particular 2-6 carbonatoms, m and n are independently 0-10 and R^(c) _(f) is a perfluoroalkylgroup of 1-6 carbon atoms. Specific examples of perfluorinated vinylethers include perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethylvinyl) ether (PEVE), perfluoro (n-propyl vinyl) ether (PPVE-1),perfluoro-2-propoxypropylvinyl ether (PPVE-2),perfluoro-3-methoxy-n-propylvinyl ether, perfluoro-2-methoxy-ethylvinylether and CF₃—(CF₂)₂—O—CF(CF₃)—CF₂—O—CF(CF₃)—CF₂—O—CF═CF₂.

Examples of perfluoroallyl ethers that can be used in the presentdisclosure include those that correspond to the formula:CF₂═CF(CF₂)—O—R_(f) wherein R_(f) represents a perfluorinated aliphaticgroup that may contain no, one or more oxygen atoms and up to 10, 8, 6or even 4 carbon atoms. Specific examples of perfluorinated allyl ethersinclude: CF₂═CF₂—CF₂—O—(CF₂)_(n)F wherein n is an integer from 1 to 5,and CF₂═CF₂—CF₂—O—(CF₂)_(x)—O—(CF₂)_(y)—F wherein x is an integer from 2to 5 and y is an integer from 1 to 5.

The resulting fluoropolymers of the present disclosure are highlyfluorinated. As used herein, “highly fluorinated” means that therepeating monomer units of the resulting polymer are perfluorinated(i.e., do not comprise any carbon-hydrogen bonds), however thefluoropolymer may comprise some carbon-hydrogen bonds, which originatefrom the fluorinated polymerizable emulsifier used, the initiator systememployed, and/or the chain transfer agent, if used.

The resulting highly fluorinated polymer may be a fluoroplastic,amorphous fluoropolymer, or a PTFE (polytetrafluoroethylene). Exemplarypolymers that would benefit from the methods as disclosed hereininclude: copolymers of TFE and HFP (FEP polymers); perfluoroalkoxycopolymers (PFA polymers); amorphous perfluorinated polymers, such asthose available under the trade designation “TEFLON AF”; meltprocessable fluoropolymers available under the trade designation “HYFLONMFA” by Solvay S.A., Ixelles, Belgium; PTFE micropowders (i.e., PTFEhaving a low molecular weight, e.g., less than 5 million grams/mole);and PTFE fine powders (i.e., those having a molecular weight, e.g.,greater than 5 million grams/mole).

In one embodiment, the polymerization of the present disclosure issubstantially free of a non-polymerizable fluorinated emulsifier (e.g.perfluoroalkanoic acids, fluorinated ethers and alkoxy ethers). In otherwords, less than 25 ppm, 10 ppm, 1 ppm, or even 0.1 ppm of anon-polymerizable fluorinated emulsifier is in the final latex.

The aqueous emulsion polymerization described herein results in adispersion of the highly fluorinated polymer particles in water (alsoknown as a latex). Generally the amount of solids of the fluoropolymerin the dispersion directly resulting from the polymerization will varybetween 3% by weight and about 40% by weight depending on thepolymerization conditions. A typical range is between 5 and 30% byweight. The particle size (z-average particle size) of the fluoropolymeris typically between 50 nm and 350 nm with a typical particle size beingbetween 100 nm and about 300 nm.

Because the polymerizable fluorinated emulsifier is polymerized into thehighly fluorinated polymer of the present disclosure, in one embodiment,the resulting latex has a low amount (in other words, less than 100 ppm,50 ppm, 25 ppm, 10 ppm, or even 1 ppm of the polymerizable fluorinatedemulsifier is in the final latex) or is substantially free of thepolymerizable fluorinated emulsifier.

After polymerization, the resulting latex may be upconcentrated toincrease the solid content. Non-ionic surfactants (e.g., those soldunder the trade designations of “TRITON” and “GENAPOL”) may be used inamounts of 2 to 10% by weight of the non-ionic surfactant to furtherupconcentrate the latex to a solid content of 40-60% as is known in theart. See for example, U.S. Pat. No. 6,833,403 (Bladel et al.) and C.A.Pat. No. 2522837 (Bladel et al.).

Alternatively, or in addition to upconcentrating the latex, thefluoropolymer particles may be isolated from the dispersion bycoagulation and dried. Such coagulation methods are known in the art andinclude chemical and physical methods, for example, using an electrolyteor inorganic salt (such as HCl, H₂SO₄, HNO₃, H₃PO₄, Na₂SO₄, MgCl₂,ammonium carbonate, etc.), using freeze-thaw cycles, applying highsheer, and/or applying ultrasonics.

In one embodiment, the process described herein may be used to generateseed polymer particles, which can be used to initiate a subsequentpolymerization. Briefly, small particles of fluoropolymer could beprepared using the polymerizable fluorinated emulsifier disclosedherein. These seed particles typically have a z-average diameter ofbetween 50 to 100 nm (nanometers). Such seed particles may be producedin a separate aqueous emulsion polymerization and may be used in anamount of 5 to 50% by weight based on the weight of water in the aqueousemulsion polymerization. Using a seed particle, in one embodiment mayresult in a core-shell particle, with the core of the particlecomprising a different composition than the shell or outer surface ofthe particle. In one embodiment, the shell comprises a fluoropolymerhaving a low melting point (for example less than 150° C.) or isamorphous. Such an embodiment would enable a core-shell particle to bemade without the addition of additional emulsifier, including thepolymerizable fluorinated emulsifier disclosed herein or anothernon-telogenic or even telogenic emulsifier.

In another embodiment, the process described herein may be used togenerate a fully polymerized polymer particle, wherein no furtherpolymerization is conducted on the polymer particles.

The polymerizable fluorinated emulsifiers of the present disclosurecomprise at least one ionic group. During polymerization, thesepolymerizable fluorinated emulsifiers are incorporated into theresulting polymer and some of these groups may be accessible forquantitation and thermal instability. The ionic groups can be detectedby techniques as is known in the art, including Fourier TransformInfrared (FTIR) spectroscopy as disclosed in U.S. Pat. No. 3,085,083(Schreyer) or by titration.

The ionic groups may lead to cracking, blistering, or corrosion at highprocessing temperatures (e.g., greater than 350° C.) and/or result inhigher metal contents in articles made from the high fluorinatedpolymers of the present disclosure. Therefore, depending on therequirements of the application in which the resulting highlyfluorinated polymer is to be used, the highly fluorinated polymer of thepresent disclosure may be post-fluorinated so as to convert anythermally unstable groups from the polymer as well as from any residualpolymerizable fluorinated emulsifier into stable CF₃ end groups.

In one embodiment, there is no need for post treatment to remove thepolymerizable fluorinated emulsifier from the fluoropolymer latex,and/or the waste water streams since the polymerizable fluorinatedemulsifier is polymerized into the highly fluorinated polymer.

Post-fluorination techniques are known in the art. Described in forexample EP 222945 (Buckmaster et al.), U.S. Pat. No. 6,541,588(Kaulbach), or DE 199 03 657 (Kaulbach et al.), herein incorporated byreference. Briefly, the coagulated fluoropolymer is subjected to anatmosphere containing fluorine (typically diluted down to 5-20% in acarrier gas, such as nitrogen) to convert unstable end groups, ifpresent in unsuitable amounts, to stable fluorinated end groups (such asto —CF₃ groups). Generally, the mixture is heated at a temperature belowthe melting range of the polymer, for example 50 to 250° C. or even100-180° C. The fluorination is continued until at least 90-95% of allpolar groups are removed. For example, the fluoropolymer will be postfluorinated such that the amount of polar end groups in thefluoropolymer other than CF₃ is less than 80 per million carbon atoms,less than 40 per million carbon atoms, or even less than 20 ppm permillion carbon atoms.

Not only will the post fluorination assist with removal of the —C(O)OHand —S(O)(O)OH groups, but it may also treat groups include —C(O)NH₂,—C(O)OR, CH₂OH, —CF═CF₂, and —C(O)F groups, which may appear duringprocessing (e.g., exposure to heat or ammonia) or from the presence ofthe initiator used.

The post-fluorination of the dried polymer, may be conducted onagglomerates, melt-pellets, or even films. Post-fluorination ofagglomerates is beneficial compared to melt-pellets since there is noabrasion from the reactors enabling low metal-contents and thefluorination times are shorter. Post-fluorinated agglomerates can bemelt-pelletized later on.

If polymer polymerized with SO₃ ⁻-containing polymerizable fluorinatedemulsifier are post-fluorinated, the fluorination may take longer time,nevertheless the fluorination conditions should be selected that themelt-flow index (MFI) should not change more than 10% compared to thenon-post-fluorinated material.

Because the highly fluorinated polymer is post-fluorinated to removeionic end groups, in one embodiment, the metal ion content of theresulting polymer may be low. For example, less than 500 ppb (parts perbillion), or even less than 100 ppb of metal ions such as Na, Ca, Al,Fe, Cr, Ni, and W. The metal ion content can be determined by combustionand induction coupled plasma (ICP) analysis.

In the present disclosure, the polymerizable fluorinated emulsifier isused to stabilize the growing polymer during polymerization. Yet, a lowlevel of polymerizable fluorinated emulsifier is used along withpost-fluorination, so that the resulting properties of the final highlyfluorinated polymer are substantially the same as those which werepolymerized with a non-polymerizable fluorinated emulsifier. For,example, after post-fluorination, the melting point of the highlyfluorinated polymer made as disclosed herein with a polymerizablefluorinated emulsifier, should be substantially the same, (i.e., lessthan 5° C., 4° C., 3° C., or even 2° C. difference) than the samepolymer made with a non-polymerizable non-telogenic fluorinatedemulsifier (e.g., perfluoroalkanoic acids and their salts or fluorinatedethoxylated carboxylic acids and their salts).

In one embodiment of the present disclosure, the resulting dried highlyfluorinated polymer made by the processes disclosed herein issubstantially free of a non-polymerizable fluorinated emulsifier. Inother words, the highly fluorinated polymer comprises less than 10 ppm,5 ppm, 1 ppm, 0.5 ppm, 0.1 ppm, 50 ppb (parts per billion) 10 ppb oreven no non-polymerizable fluorinated emulsifier. The amount ofnon-polymerizable fluorinated emulsifiers in the polymer can bedetermined by volatizing or extracting the emulsifiers from the highlyfluorinated polymer using techniques known in the art.

EXAMPLES

Advantages and embodiments of this disclosure are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. In theseexamples, all percentages, proportions and ratios are by weight unlessotherwise indicated.

All materials are commercially available, for example from Sigma-AldrichChemical Company; Milwaukee, Wis., or known to those skilled in the artunless otherwise stated or apparent.

These abbreviations are used in the following examples: g=gram,kg=kilograms, min=minutes, mol=mole; cm=centimeter, mm=millimeter,ml=milliliter, L=liter, psi=pressure per square inch, MPa=megaPascals,and wt=weight.

Methods

Melt Flow Index (MFI)

The MFI of the fluoropolymers, reported in g/10 min, was measured at atemperature of 372° C. following a method similar to that described inDIN EN ISO 1133 with a support weight of 5.0 kg. The MFI was obtainedwith a standardized extrusion die of 2.095 mm diameter and a length of8.0 mm.

Melting Point

Melting peaks of the fluoropolymers were determined following a methodsimilar to that described in ASTM 4591 by means of Perkin-Elmer DSC 7.0(Perkin-Elmer, Waltham, Mass.) under nitrogen flow and a heating rate of10° C./min. The indicated melting points relate to the melting peakmaximum.

Particle Size Determination

The latex particle size determination was conducted by means of dynamiclight scattering (Malvern Zetasizer 1000 HAS, Malvern, UK) following amethod similar to that described in ISO/DIS 13321. The reported averageparticle size is the z-average. Prior to the measurements, the latexesas yielded from the polymerisations were diluted with 0.001 mol/LKCl-solution, and the measurement temperature was 20° C. in all cases.

Total Endgroup

The amount of carbonyl content (e.g., COO⁻/COF) was conducted by theintegrated absorbance ratio a FTIR spectrum of the fluoropolymer using aFa Nicolet DX510 FTIR spectrometer using OMNIC software (ThermoFisherScientific, Waltham, Mass.) using techniques as described in EP Pat. No.222945 (Buckmaster et al.), U.S. Pat. No. 4,687,708 (Betzar) and U.S.Pat. No. 4,675,380 (Buckmaster et al.).

PPVE Content

The amount of perfluoro (n-propyl vinyl) ether (PPVE) interpolymerizedin the resulting polymer was calculated from the ratio of the PPVEabsorbance at 993 cm⁻¹ to a reference peak at 2365 cm⁻¹ using FTIR. Theratio of these two peaks multiplied by 0.95 gives the % (m/m) PPVE. Theremainder of the resulting polymer was interpolymerized TFE.

Polymerizable Fluorinated Emulsifier Determination

A BF₃ methanol complex was used to derivatize theCF₂═CF—O—(CF₂)₃—O—CF₂—COO⁻ molecule in the dispersion to its methylesterform. The content of the polymerizable fluorinated emulsifier in thelatex sample was determined by headspace gas chromatography with a massspectrometer detection. A fused silica capillary column having an innerdiameter of 0.32 mm coated with a 1% vinyl/5% phenyl/94% dimethylpolysiloxane (1.8 μm film thickness) was used. The results are reportedas the methyl ester form.

Comparative Example A

The polymerization experiment was performed in a 40-L kettle equippedwith an impeller agitator and a baffle. The kettle was evacuated andthen charged with 30 L of deionized water and set to 63° C. Into theoxygen free kettle, 210 g (30%) of a non-polymerizable fluorinatedemulsifier ([CF₃—O—(CF₂)₃—O—CHF—CF₂—C(O)O⁻NH⁴⁺, prepared as described inU.S. Pat. No. 7,671,112 Hintzer, et al.) was added under stirring. Thekettle was pressurized with TFE up to 13 bar, after which, 0.1 bar ofethane (a chain transfer agent) and 190 g of PPVE were added. Thepolymerization was started with 1.3 g APS (ammonium persulfate,(NH₄)₂S₂O₈). Over the course of polymerization 7.5 kg TFE and 300 g PPVEwere consumed during 4 hrs.

This process yielded a latex having a solid content of 21% by wt and anaverage particle size of 81 nm. The measured composition of theresulting polymer was 4.3 wt % PPVE and 95.7 wt % TFE.

The polymer was coagulated by the addition of HCl, washed, and thendried. The dried polymer had a melting point of 306° C., MFI (372° C./5kg)=1.9 g/10 min, and a total endgroups amount of 70 ppm.

Example 1

The same set-up and similar conditions as described in ComparativeExample A was used with the following exceptions. The non-polymerizablefluorinated emulsifier was replaced by 10.9 g ofCF₂═CF—O—(CF₂)₃—O—CF₂—COO⁻Na⁺ (which was received as in its methylesterform from Anles/St. Petersburg, Russia and converted in-house to thesodium salt form). 5 g of the CF₂═CF—O—(CF₂)₃—O—CF₂—COO⁻Na⁺ wasprecharged into the kettle at the start of polymerization and theremainder was continuously fed into the reactor until 2 kg of the TFEwas consumed. The polymerization was started with 0.7 g of APS. After4.5 hrs, 3.4 kg of TFE and 120 g of PPVE were consumed.

This process yielded a latex having a solid content of 9.6% by weight,and an average particle size of 75 nm. The amount of polymerizablefluorinated emulsifier in the latex was determined following thepolymerizable fluorinated emulsifier determination method above. Thelatex was found to comprise 2 μg/g of the polymerizable fluorinatedemulsifier. The measured composition of the resulting polymer was 4.1 wt% PPVE and 95.9 wt % TFE.

The polymer was coagulated by the addition of HCl, washed and thendried. The dried polymer had a melting point of 302° C., MFI (372° C./5kg)=75 g/10 min, and a total endgroup amount of 450 ppm.

100 g of the coagulated and dried polymer from above waspost-fluorinated at 215° C. with a 90 to 10 ratio of N₂ to F₂ for atotal of 300 min. The resulting polymer had a melting point of 303° C.,MFI (372° C./5 kg)=72 and a total endgroup amount of 53.

Example 2

The same set-up and similar conditions as described in ComparativeExample A was used with the following exceptions. The non-polymerizablefluorinated emulsifier was replaced by 21 g of CF₂═CF—O—(CF₂)₄SO₃NH₄(prepared from CF₂═CF—O—(CF₂)₄SO₂F as disclosed in U.S. Pat. No.6,624,328 (Guerra) and converted to the ammonium salt form). After 5 h3.8 kg TFE and 150 g PPVE were consumed.

This process yielded a latex having a solid content of 12% by weight,and an average particle size of 80 nm. The measured composition of theresulting polymer was 3.9 wt % PPVE and 6.1 wt % TFE.

Foreseeable modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes. To the extent that there is a conflict or discrepancy betweenthis specification and the disclosures incorporated by reference herein,this specification will control.

What is claimed is:
 1. An aqueous mixture comprising: a polymerizationproduct of a perfluorinated monomer and a polymerizable fluorinatedemulsifier wherein the polymerizable fluorinated emulsifier is selectedfrom the group consisting of: CF₂═CF—O—(CF₂)_(p)—O—(CF₂)_(r)—Y where Yis COOM or SO₃M, p is an integer selected from at least 3 and at most 6,r is an integer selected from at least 1 and at most 6, and M is H, analkali metal, or NH₄, wherein the resulting polymer comprises aperfluorinated backbone.
 2. The aqueous mixture of claim 1, wherein theperfluorinated monomers are selected from the group consisting of:tetrafluoroethylene, hexafluoropropylene, perfluoroalkoxy alkenes,perfluoro alkyl vinyl ethers, perfluoroalkoxy vinyl ethers,perfluoro-5-oxa-hept-6-ene sulphonic acid fluoride, CF₂═CFO(CF₂)₅CN, andcombinations thereof.
 3. The aqueous mixture of claim 1, wherein theaqueous mixture is substantially free of a non-polymerizable fluorinatedemulsifier.
 4. The aqueous mixture of claim 1, wherein the aqueousmixture is substantially free of saturated fluorinated emulsifier. 5.The aqueous mixture of claim 1, wherein the polymerizable fluorinatedemulsifier is CF₂═CF—O—(CF₂)₃—O—CF₂—COOM, where M is H, an alkali metal,or NH₄.
 6. The aqueous mixture of claim 1, wherein an amount ofpolymerizable fluorinated emulsifier is at least 50 parts per millionbased on a total amount of the perfluorinated monomer.
 7. The aqueousmixture of claim 1, wherein an amount of polymerizable fluorinatedemulsifier is at most 10000 parts per million based on a total amount ofthe perfluorinated monomer.